microDXP Technical Reference Manual
Version 3.15
October 7, 2019
24
Digital Gain is used for MCA scaling and
calibration
Table 2-2: Gain Modes supported by the new ‘blue’ microDXP
2.2.2 Serial Number
In ProSpect, the serial number is automatically read at startup. It is displayed along the
bottom of the main window, and in the
Information
tab of the
Board Information
dialog.
The RS-232 command to read the serial number is 0x48. Please refer to the RS-232
Command Specification for details.
2.2.3 On-Board Temperature
The microDXP hardware includes an I2C thermometer. The temperature reading is not
accessible in ProSpect.
The RS-232 command to read the on-board temperature is 0x41. Please refer to the RS-
232 Command Specification for details.
2.3 Global Settings and the GLOBSET
The GLOBSET, specified in Appendix BAppendix A, contains global settings including
detector/preamplifier settings and system settings. There is only one GLOBSET—these
settings are used for all peaking times and MCA formats.
The GLOBSET includes detector/preamplifier settings, advanced processor settings, run
control settings and diagnostic control settings.
In ProSpect, GLOBSET settings are accessed via the
Detector
and
Advanced
tabs of the
Settings
panel. Because these settings are global, changes are simultaneously applied and
saved to nonvolatile memory via the
[Apply / Save]
button.
2.3.1 Preamplifier Settings
The microDXP’s analog hardware, firmware and a few settings must be configured to
match the preamplifier.
2.3.1.1
Preamplifier Type
Please refer to §4.1 for more detailed description of charge-sensitive preamplifier
topologies. Briefly, RC-feedback preamplifiers use resistive feedback to provide a
continuous discharge path for the feedback capacitor, resulting in a characteristic decay
time, e.g. 50
s. Reset preamplifiers employ a switch to periodically discharge the
capacitor very quickly, resulting in a periodic ‘staircase’ waveform with many x-ray steps
between each reset, which rapidly returns the signal to its starting point.
The microDXP must have DSP and FPGA code pre-loaded in non-volatile memory that is
appropriate for the preamplifier type used, and the microDXP hardware must be set type
via a miniature DIP switch (refer to Appendix A for the switch location and settings).
In ProSpect, the preamplifier type corresponding to the loaded firmware is displayed in the
Detector tab of the Settings panel. The DSP code variant (DSP parameter CODEVAR) is
always even, e.g. “0”, for reset-type preamplifiers, and odd, e.g. “1”, for RC-feedback
preamplifiers.
